The present invention relates to electronics assemblies, and is primarily concerned with racked assemblies. Many such assemblies will be located in racks for housing in for example nineteen inch cabinets, or other size cabinets such as twenty three inch or metric cabinets. The assemblies may for instance be employed as servers for a number of systems, for example in local area networks (LANs), wide area networks (WANs), telecommunications systems or other operations such as database management or as internet servers.
Such an assembly will typically comprise a supporting frame that houses a motherboard or backplane and a number of daughterboards or module cards that extend in planes generally perpendicular to the plane of the motherboard and which are connected to the motherboard by connectors, e.g. high density connectors, so that the daughterboards can simply be located on guides and pushed toward the motherboard in order to connect them to it.
In addition, the motherboard may need to be removed for general maintenance purposes, upgrading or the like and so the frame of the assembly will normally provide for removal of the motherboard therefrom and re-insertion therein.
One problem that can be encountered is in alignment of the daughterboards and the motherboard after the boards have been removed and replaced. For example, it is quite possible for the positional tolerance of the motherboard within the frame of the assembly, and for the tolerance of the guides for the daughterboards within the frame to be relatively large. In addition, parts of the frame itself can flex due to the forces applied to it during handling. All these tolerances add to one another, with the result that it is possible for the variation in the alignment between the connectors on the daughterboards and those on the motherboard to exceed the maximum acceptable positional deviation for the electrical connectors.
According to one aspect the present invention provides an electronics assembly which comprises:
(i) a frame;
(ii) a motherboard that is removable from the frame;
(iii) one or more daughterboards that extend in a plane generally perpendicular to the plane of the motherboard; and
(iv) a plurality of elongate guides for the daughterboards to enable each daughterboard to be moved toward the motherboard into engagement therewith and away from the motherboard out of engagement therefrom;
wherein the motherboard has at least one location element thereon, which can engage one of the elongate guides in order to locate the guides and the motherboard with respect to one another.
By locating the motherboard directly with the card guides for the daughterboards it is possible to decrease misalignment of the connectors on the motherboard and on the daughterboards significantly since any misalignment of the motherboard within the assembly frame and any slight flexing of the frame that might cause those parts thereof that support the card guides to become displaced can be ignored insofar as alignment of the motherboard and daughterboard connectors is concerned.
The problems of misalignment are particularly severe in assemblies where the motherboard can be removed from, or inserted in, the frame by movement in its own plane. For example the motherboard may be located in, and fixed to, a substantially tray-shaped holder that can be slid into and out of the frame via an elongate slot. For ease of assembly and disassembly it is often desirable to dispense with screw-fixing in such circumstances and instead to rely on a stop that abuts the tray-shaped holder to locate the motherboard correctly within the frame and some form of manually engageable fixing arrangement to fix the motherboard and holder in place. Such an arrangement has the disadvantage that the potential degree of misalignment between the motherboard and the daughterboards is substantially greater than when employing screw fixings and alignment of the daughterboards with the motherboard can be impossible to achieve to the tolerance required by the connectors for correct mating. According to the invention, however, the relevant card guides themselves effectively provide a stop for limiting insertion of the motherboard.
In such an arrangement the location elements on the motherboard may stand up from the printed circuit board forming the motherboard so that they can engage their corresponding card guides but the guides will allow the motherboard to be removed from, or inserted in, the frame without inadvertently hitting any other components on the motherboard.
The assembly will normally contain an array of daughterboards each located between a pair of card guides. It is not necessary for all the card guides to extend sufficiently close to the motherboard to engage a location element, but only for a minimum of one and preferably of two card guides which are in positions corresponding to the positions of the location elements to extend that closely to the motherboard while the other card guides may terminate a greater distance away. Clearly it is desirable if the positions of the location elements on the motherboard are separated by a significant fraction of the overall dimensions of the motherboard, for example by at least ⅓ or at least xc2xd the overall dimensions in order to provide improved resistance to relative rotation of the motherboard and the card guides about an axis normal to the plane of the motherboard. Normally, the daughterboards will all be located in the same region of the frame, for example in a single sub-enclosure, so that if the frame as a whole is subjected to any strain by insertion of the motherboard into engagement with the card guides, all the card guides will move together as the frame flexes slightly and so will stay in alignment with the motherboard. If, however, daughterboards are provided in different sub-enclosures in the frame, it may be necessary for additional location elements for the daughterboards in each sub-enclosure to be provided.
The location elements on the motherboard may, for example, be in the form of protuberances, for instance pins, that become located in recesses in the corresponding card guides when the motherboard is in position. It is not necessary for each location element to prevent relative movement of the motherboard and the card guides in all directions in the plane of the motherboard, but instead, engagement of one location element on the motherboard with the corresponding card guide may prevent relative movement of the motherboard and the guides in a direction perpendicular to the direction in which movement is prevented by engagement of the other location element and its corresponding guide. In one example, engagement of one location element on the motherboard with its corresponding card guide may prevent relative movement of the motherboard and the corresponding card guide in two orthogonal directions (in the plane of the motherboard) while engagement of the other location element with its guide need only prevent movement of the motherboard in one direction, that is to say, engagement of the other location element with its card guide simply needs to prevent any rotation of the motherboard about the first location element.
The invention is applicable to any assembly comprising a motherboard and a number of daughterboards or module cards irrespective of their orientation, for example in a conventional orientation in which the motherboard is arranged in a vertical plane at the back of a cabinet and the daughterboards are arranged, either in a vertical or horizontal plane, so that they can be removed or inserted in a horizontal direction from the front of the cabinet. The invention is also applicable to a new design of assembly in which the motherboard is located within the assembly frame substantially horizontally, especially beneath the daughterboards, and the daughterboards are arranged in an array in vertical planes. In such a case the assembly may need to be removed from the cabinet in one piece in order to remove the daughterboards, in which case it can be supported on telescopic sliders.
According to another aspect, the present invention provides a frame for an electronics assembly which comprises:
(i) a location in which a planar motherboard can be received; and
(ii) a plurality of guides that extend in a direction generally normal to the plane of the motherboard when it is received in the frame in order to enable a plurality of daughterboards to be located in the frame in engagement with the motherboard, at least one of the guides having a location element thereon that can engage a corresponding location element on a motherboard in order to locate the guides and the motherboard with respect to one another.
According to yet another aspect, the invention provides a method of installing a motherboard in a frame for an electronics assembly comprising a plurality of guides for daughterboards, the guides extending generally normal to the plane of the motherboard, which method comprises:
(i) sliding the motherboard into the frame; and
(ii) causing a location element on the motherboard to engage a corresponding location element on at least one of the guides in order to locate the guides and the motherboard with respect to one another.